1. Field of the Invention
The present invention relates to a filter, a duplexer, and a communication device for use in radio communication or the transmission/reception of electromagnetic waves, in e.g. a microwave band or a millimeter wave band.
2. Description of the Related Art
As an example of a miniaturizable resonator which is used in a microwave band or millimeter wave band, a spiral resonator is disclosed in Japanese Unexamined Patent Application Publication No. 2-96402. This spiral resonator provides a longer resonance line in a given occupied area by forming the resonance line into a spiral shape, thereby achieving an overall size-reduction.
In a conventional resonator, one half wavelength line constitutes one resonator. Therefore, in a conventional resonator, the region where electrical energy is concentrated and stored, and the region where magnetic energy is concentrated and stored are separated from each other and unevenly distributed at specific areas of a dielectric substrate. More specifically, the electrical energy is stored in the vicinity of an open end of the half wavelength line, while the magnetic energy is stored in the vicinity of the center portion of the half wavelength line.
The resonator constituted of one microstrip line has a drawback, in that its characteristics are inevitably deteriorated by the edge effect which the microstrip line intrinsically possesses. Specifically, when viewing the line in cross-section, current is concentrated in the edge portions of the line (both ends in the width direction, and the upper and lower ends in the thickness direction of the line). Even if the film-thickness of the line is increased, the problem of the power loss due to the edge effect inescapably occurs, since the edge portions at which the current is concentrated can not be widened by an increase in the film-thickness.
Accordingly, the present applicants have applied for European Patent Application Publication No. EP 1 014 469 A2, which discloses a device which is capable of very effectively suppressing the power loss due the edge effect in the lines, and is also capable of achieving an overall size-reduction of the device.
In response to the above requirements, the present invention provides a filter and a duplexer which are capable of very effectively suppressing the power loss due to the edge effect in the lines, which allow a greater reduction in their overall size, and which provide desired filter characteristics, and further to provide a communication device including the filter and/or the duplexer.
The present invention, in a first aspect, provides a filter comprising at least three resonators arranged on a substrate, each of which resonators is an aggregate of a plurality of lines each having a spiral shape, in each of which the two ends of at least a portion of the plurality of lines are disposed respectively at substantially the inner and outer periphery portions of the aggregate and are arranged, preferably symmetrically, around a predetermined point of the substrate, and in each of which the plurality of lines are disposed so as not to intersect each other. In this filter, the spiral direction of the spiral lines in at least one resonator is set to be opposite to that of the spiral lines in the other resonators. These features allow an attenuation pole to be arbitrarily formed on the higher frequency side or the lower frequency side of a pass band when using this filter as a band pass filter.
The present invention, in a second aspect, provides a filter comprising at least three resonators arranged on a substrate, in each of which resonators the two ends of a plurality of lines are disposed respectively at substantially the inner and outer periphery portions, arranged preferably symmetrically around a predetermined point of a substrate, and in each of which the plurality of lines are disposed so as not to intersect each other. This filter further comprises input/output portions, and a coupling conductor provided at the inner periphery portion of at least one resonator. The inner periphery portion and the input/output portions are capacitively coupled by the coupling conductor. As in the case of the first aspect, these features allow an attenuation pole to be arbitrarily formed on the higher frequency side or the lower frequency side of a pass band.
The present invention, in a third aspect, provides a duplexer including a filter in accordance with the first or second aspect, usable as a transmitting filter or a receiving filter, or including filters in accordance with the first or second aspect, usable as a transmitting filter and a receiving filter. This makes it possible to provide a predetermined pass band, to reduce the insertion loss, to achieve an overall size-reduction of the filter, and to reliably prevent interference at an adjacent regions between a transmission band and a reception band.
The present invention, in a fourth aspect, provides a duplexer wherein the spiral direction of the spiral lines in the resonators constituting a transmitting filter and the spiral direction of the spiral lines in the resonators constituting a receiving filter are set to be opposite to each other. This feature allows the isolation between the transmitting filter and the receiving filter to be improved.
In a duplexer in accordance with the present invention, a filter which is constructed by arranging, on a substrate, at least three resonators, in each of which a plurality of spiral lines is distributed, and by capacitively coupling an inner periphery portion, defined by a plurality of lines of at least one resonator, to input/output portions of the filter, is preferably used as one of the transmitting filter and the receiving filter. On the other hand, the filter constructed by arranging at least three resonators in which a plurality of spiral lines having mutually identical spiral directions are distributed, is preferably used as the other filter.
By virtue of the described features, the present invention provides a duplexer which combines a filter having an attenuation pole on the lower frequency side of a pass band, and one having an attenuation pole on the higher frequency side of the pass band.
The present invention, in a fifth aspect, provides a communication device using the above-described filter or duplexer. This makes it possible to achieve an overall size-reduction thereof, to reduce the insertion loss at high-frequency transmission/reception portions, to reliably prevent the interference between adjacent bands, and to improve communication qualities such as the noise characteristics and the transmission speed.
The above and other objects, features, and advantages of the present invention will be clear from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.